Investigations of lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) in the pathogenesis of pulmonary fibrosis in idiopathic pulmonary fibrosis and the acute respiratory distress syndrome, and of dermal fibrosis inscleroderma.

Fibrotic diseases such as idiopathic pulmonary fibrosis (IPF) and scleroderma are associated with high morbidity and mortality, with outcomes largely unaffected by current therapies. Improved understanding of the biologic processes involved in development of fibrosis in these diseases, and more complete identification of the molecular mediators driving these processes, are urgently needed to develop effective new therapies. We have recently found that the potent lipid mediators lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) direct multiple processes fundamentally involved in fibrogenic responses to injury, including epithelial cell apoptosis, vascular leak, and fibroblast recruitment and persistence.

We have found that LPA signaling through one of its receptors, LPA1, is critically required for the development of pulmonary and dermal fibrosis in mice following bleomycin-induced injury of these tissues: LPA1-deficient mice are dramatically protected from fibrosis in these commonly used models of IPF and scleroderma. We have also found that LPA levels are increased in the BAL fluid of patients with established IPF, that LPA1 is highly expressed by fibroblasts recovered from IPF BAL, and that pharmacological antagonism of LPA1 markedly reduces fibroblast responses ex vivo to the chemotactic activity of IPF BAL. In our studies of S1P in fibrotic disease, we have recently demonstrated that inhibition of S1P-S1P1 signaling dramatically worsened vascular leak induced by bleomycin lung injury. In these studies, we found that mice developing increased leak from S1P1 antagonism also went on to develop markedly increased lung fibrosis following bleomycin injury. We are now pursuing multiple studies described in the Research Projects section of this site, to further define the roles of these important mediators, and potential targets for novel therapies, in both mouse models and translational studies of fibrotic diseases.

Investigations of HIV pathogenesis in a humanized mouse model of HIV infection. The development of a safe and effective HIV vaccine is a global health priority, but will require improved understanding of the immunopathogenesis of HIV infection. An ideal animal model in which to study the pathogenesis of HIV infection has been elusive, however. There has been increased interest in humanized mouse models of HIV infection, although the absence of robust anti-HIV human immune responses in these models to date has suggested that they are not yet ready to test immune responses to vaccine candidates. Recently, we and others have developed an improved humanized mouse model of HIV by transplanting human CD34+ stem cells and autologous human thymic grafts into immunodeficient mice. In this model, we have achieved robust repopulation of mouse lymphoid tissues with human immune cells, and have generated robust anti-HIV cellular and humoral immune responses in these humanized mice. We believe this improved humanized mouse model will allow us to study questions regarding the biology of HIV not readily approachable through human studies. Currently, we are using our humanized mouse model of HIV infection to investigate the immunogenecity and protective efficacy of several candidate HIV vaccines, as well as the mechanisms of viral dissemination, of HIV-induced immune activation, and of HIV-induced immune dysfunction. Specific studies are described in the Research Projects section of this site. In addition to our own investigations, we have recently initiated a humanized mouse program for the Harvard University Center for AIDS Research (HU CFAR) and the Ragon Institute of MGH, MIT and Harvard, through which we are making humanized mice available to HU CFAR and Ragon collaborators.

Research Projects

Investigations of lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) in the pathogenesis of pulmonary fibrosis in idiopathic pulmonary fibrosis and the acute respiratory distress syndrome, and of dermal fibrosis inscleroderma.

Generation of mice in which LPA1 expression is deleted only in one specific cell type at a time using the Cre-lox system of site-specific recombination, to determine the specific contributions of LPA1 expressed by epithelial cells, endothelial cells, or fibroblasts to the pathogenesis of pulmonary fibrosis.

Evaluation of the role of LPA and LPA1 in epithelial cell apoptosis in the pathogenesis of pulmonary fibrosis.

Comparison of the frequencies of single nucleotide polymorphisms (SNPs) in 5 LPA receptors, 6 enzymes involved in LPA synthesis, and 3 enzymes capable of degrading LPA between persons with and without IPF to investigate whether polymorphisms in these genes contribute to individuals’ risk for IPF.

Evaluation of the role of LPA and LPA1 in the pathogenesis dermal fibrosis in the bleomycin mouse model of scleroderma.

Investigation of the mechanism through which S1P-S1P1 signaling protects against lung injury in vivo, using mice in which LPA1 expression is deleted only in one specific cell type at a time

Evaluation of whether manipulation of S1P levels can prevent lung injury in vivo.

Investigation of the mechanistic link between vascular leak and the development of fibrosis after lung injury.

Investigations of HIV pathogenesis in a humanized mouse model of HIV infection.

Investigation of the nature, quality and protective efficacy of immune responses to three HIV vaccines: (1) Adrithiol (AT)-2-inactivated HIV; (2) the recombinant adenovirus serotype 5 (rAd5) vector HIV vaccine used in the Merck STEP trial; and (3) the recombinant canarypox vector/glycoprotein 120 subunit HIV vaccine used in the MOPH-TAVEG trial. These studies will be followed by investigations of whether we can improve the protective efficacy of the immune responses produced by these vaccines by manipulating gene expression in the human immune cells of the vaccinated mice.

Investigation of the role of the PD-1 pathway, a member of the B7-CD28 family of cell surface receptors that negatively regulates T cell activity, in immune dysfunction induced by HIV infection in vivo, by testing the hypothesis that inhibiting the PD-1 pathway will reinvigorate “exhausted” CD8+ T cells in vivo and lead to better control of HIV replication.

Development of the ability to genetically modify the human CD34+ hematopoietic stem cells (HSCs) used to reconstitute humanized mice, to develop a novel system to molecularly dissect the human immune system and its interaction with HIV and other pathogens in vivo. We are initially transducing HSCs with rhesus monkey or mutant human versions of the anti-HIV restriction factors tripartite motif protein 5a (TRIM5a), or the apolipoprotein B mRNA-editing enzyme catalytic polypeptide 3G (A3G), to evaluate the ability of these restriction factors to inhibit HIV-1 infection in human cells in vivo.

Investigation of viral dissemination in vivo by visualizing the migratory behavior of both HIV itself and of human T cells and dendritic cells in the lymph nodes of our humanized mice using multiphoton intravital microscopy (MV-IVM), performed in collaboration with CIID investigatorThorsten Mempel. Using fluorescently labeled virus, we are investigating how HIV is delivered to the lymph node either as a free virus or a virus associated with dendritic cells or T cells. Using an HIV mutant inducing the expression of GFP in infected cells, we are investigating the anatomy of HIV spread within the lymph node over time.

Collaborations with investigators from Harvard University Center for AIDS Research (HU CFAR) and the Ragon Institute of MGH, MIT and Harvard.

In vivo assessment of the fitness costs to HIV of CTL escape mutations.

Assessment of the impact of immune activation by HIV-encoded TLR ligands on HIV immunopathogenesis.

Assessment of the role of Th17 cells in protection against HIV infection.

Use of HIV mosaic proteins to elicit T cell responses against target and escape epitopes.

Assessment of the efficacy of siRNA-based microbicides to protect against vaginal transmission of HIV.